The production of fluid hydrocarbons from wells involves a technology based on a long history of experience. While wells within some geographic regions are capable of producing under naturally induced reservoir pressures, more commonly encountered are well facilities which employ some form of an artificial lift production procedure. Among those latter lifting techniques are a non-pumping, gas lifting variety where, in general, a cycled opening and closing of the well is carried out. Under this approach, natural gas pressures, whether artificially or naturally induced, are permitted to build at a closed well in conjunction with an inflow of liquids, usually present as some combination of oil and saltwater. As a proper combination of pressure and liquid in flow quantity develops, the well is opened to a gathering system or receiving facility. Such gathering systems will vary, but conventionally include a gas/liquid separator, one or more sales lines, and a tank or reservoir for collecting liquids issuing from the well during its open interval.
The terminology associated with well production, in many instances representing somewhat colorful argots, has varied somewhat in meaning as technology has progressed over the years. All cyclical production now is generally referred to as "intermitting", and the intermitting process provides for the provision of alternating on-cycles or states and off-cycles or states. Where a well is closed as a consequence of the termination of cyclical control, it is said to be "shut-in". Conventionally, the cyclical opening and closing procedure is carried out with a gas driven motor valve which when utilized in conjunction with opening conduits to a gas sales line is referred to as a "sales valve".
The timing involved in intermitting a well has long been considered critical. Production of the well occurs only during an on-cycle which will remain for a relatively short interval following which the off-cycle is carried out. The deriving of the timing of these cycles has always been a taxing endeavor to well technicians. Many production parameters are considered for this task no two wells exhibiting the same performance signature and, importantly, the performance signature of any given well changing with time. This in the past has called for the presence of the well technician at the well location on a quite frequent basis to observe the many well parameters involved including tubing pressure, casing pressure, sales line pressure, and many other heuristic details. A failure of the intermitting process results in an excessive quantity of liquids within the tubing string referred to generally as a "loading up" of the well. This condition represents a failure which may be quite expensive to correct.
Many well installations employ a plunger method of artificial lift wherein a piston which is referred to as a "plunger" is slideably installed within the tubing string of the well and is permitted to travel the entire length of that tubing string in conjunction with the on-cycle and off-cycle of the well. The most important requirement for plunger lift practice is that the plunger itself arrive at the well head in the course of each on cycle. Generally, plunger lift is classified as a separate and distinct method of artificial lift, although in some instances, it serves as only a temporary means of keeping a well commercially feasible prior to the installation of another method of artificial lift. Some of the more common applications of plunger lift are as follows:
(1) utilization in a high gas-liquid ratio well to maintain production by cyclical operation; PA1 (2) utilization in a gas well to unload accumulated liquids; PA1 (3) utilization in an oil or gas well to keep the tubing string clean of paraffin, scale, and the like; and PA1 (4) utilization in conjunction with intermittent gas lift to reduce liquid fall-back. PA1 assigning first values corresponding with the rate of movement of the plunger from the lower region to the wellhead which represents normal plunger performance; PA1 assigning second values less than the first values corresponding with the rate of movement of the plunger from the lower region to the wellhead which represent slow plunger performance; PA1 assigning a predetermined value for the time interval of the on-state; PA1 assigning a predetermined value for the time interval of the off-state; PA1 actuating the control valve to transition from an off-state to an on-state; PA1 then detecting the arrival of the plunger at the wellhead prior to expiration of the time interval of the on-state, and determining the time elapsed from that actuation; PA1 determining the presence of any coincidence with the assigned second values of plunger rate of movement corresponding with the time elapsed; PA1 then increasing the predetermined value for the time interval of the off-state by a predetermined first time increment when a coincidence with the assigned second value is present; and PA1 terminating the on-state in response to plunger detection, and actuating the control valve to transition from the on-state to the next off-state in response to the on-state termination. PA1 providing a tank control valve coupled for regulating the flow of fluid hydrocarbon from the well tubing string to the tank, the tank control valve being actuable to establish a tank on-state and further actuable to close fluid flow communication between the tubing string and the tank; PA1 assigning select values corresponding to the rate of movement of the plunger from the lower region to the wellhead which represent predetermined plunger performance; PA1 assigning a value for a tank-on-time interval; PA1 assigning a predetermined value for the time interval of the on-state; PA1 assigning a predetermined value for the time interval of the off-state; PA1 actuating the sales control valve to transition from an off-state to an on-state and commencing the timing of the on-state; PA1 providing an arrival signal when the plunger arrives at the wellhead subsequent to the actuation of the sales control valve in transition to the on-state; PA1 actuating the sales control valve to the off-state when the time interval of the on-state is concluded in the absence of the arrival signal; PA1 determining the presence of a tank cycle condition when the time interval of the on-state is concluded in the absence of the arrival signal; PA1 actuating the tank control valve in response to the tank cycle condition to establish the tank on-state and commencing the timing of the tank on-time interval; and PA1 actuating the tank control valve to close and terminate the fluid flow communication in response to the arrival signal and commencing the timing of the off-state. PA1 assigning a predetermined fixed value for the time interval of an on-cycle; PA1 assigning first values corresponding with the rate of movement of the plunger from the lower region to the wellhead which represent normal plunger performance; PA1 assigning second values corresponding with the rate of movement of the plunger from the lower region to the wellhead which represent fast plunger performance; PA1 assigning a predetermined initial value for the time interval of the off-cycle; PA1 assigning a predetermined minimum value for the time interval of the off-cycle; PA1 actuating the control valve to transition from the off-cycle to the on-cycle; PA1 providing an arrival signal when the plunger arrives at the wellhead subsequent to the actuation of the control valve to transition to the on-cycle; PA1 determining the presence of a fast plunger rate when the arrival signal occurs within a time interval from the on-cycle control valve actuation corresponding with the second values; PA1 decreasing the initial value for a time interval of the off-cycle by a predetermined increment of time in response to the determination of a fast plunger rate to derive an adjusted value for the time interval of off-cycle; and PA1 maintaining the predetermined minimum value for the time interval of the off-cycle when the adjusted value is equal thereto. PA1 actuating the sales control valve from the closed orientation to the open orientation to commence an on-cycle; PA1 timing the on-cycle for an on-cycle control interval; PA1 timing an afterflow extension of the on-cycle for an afterflow delay interval; PA1 actuating the sales control valve from the on-cycle to the off-cycle at the termination of the afterflow delay interval; PA1 timing the off-cycle for an off-cycle control interval; PA1 commencing the timing of an on-cycle high line delay interval in response to the presence of the high line signal during the timing of the on-cycle and suspending the remaining time of the on-cycle; PA1 responding to the removal of the high line signal during the on-cycle high line delay interval by reinstating the on-cycle for the remaining on-cycle time; PA1 actuating the sales control valve to the closed orientation when the on-cycle high line delay interval terminates during the on-cycle control interval and maintaining the closed orientation until the subsequent removal of the high line signal; and PA1 actuating the sales control valve to the open orientation to commence an on-cycle in response to the subsequent removal of the high line signal.
The introduction of a plunger to a lift cycle provides a solid and sealing interface between the lifting gas and the produced liquid slug. This interface so provided by the plunger changes the flow pattern of the gas during a lifting cycle from the familiar ballistic shape of gas penetration of the liquid slug to a pattern wherein gas flow is possible only in the annular space between the tubing walls and the outside surface of the plunger.
Since the lift gas pressure under the plunger must be greater than the pressure created by the gas column pressure plus the liquid load above the plunger, the small quantity of gas that by-passes the plunger flows upwardly through the annular space and acts as a sweep, thus minimizing any tendency for liquid fall-back. The elimination of possible gas penetration through the center of the liquid slug and the minimization of any liquid fall-back makes the plunger application a most efficient form of intermittent production.
For a substantial period of time, control over the cyclical production of wells has been based simply upon a crude, clock-operated device. This device required hand winding and thus well location visitation by technicians on a quite frequent basis. Inasmuch as those locations are, for the most part, difficult to access areas, the earlier spring-wound controllers were the source of much frustration to the industry. That frustration commenced to end with the introduction to the industry of a long life battery operated controller by W. L. Norwood in about 1978. Described in U.S. Pat. No. 4,150,721, this seminal electronic controller provided for long term, battery operated control over wells and served to simplify the control adjustment procedure required of well technicians. Of particular importance, the controller is designed to respond to system parameters to override the cycle timing to accommodate conditions where such timing should be overridden and subsequently re-initiated on an automatic basis. Sold under the trademark "Digitrol", the controller has been seen to have had a profound impact upon well production.
In 1980, W. L. Norwood and Logic Controls Corporation introduced the microprocessor driven controller to the industry. This instrument, marketed under the trademark "Liquilift", gave the well technician a substantially expanded capability and flexibility for well control, providing for response to a substantial number of well parameters, as well as for the development of delay techniques to accommodate for temporary system excursions and the like. The initial version of the Liquilift device is described in U.S. Pat. No. 4,352,376, by Norwood, entitled "Controller for Well Installations", issued Oct. 5, 1982. Subsequently, still further upgraded versions of the initial microprocessor driven controller had been introduced to the industry and are marketed as "Liquilift II" and for dual motor valve operation, the "Liquilift II+2" and "Liquilift II+2T".
Given the substantially improved flexibility of these latter, computer driven instruments, the industry now seeks techniques for their use wherein the controller, in effect, represents the presence of a well technician at a well location on a continuous basis. With such continuous fine tuning of a well, industry anticipates a production technique which can be maximized without resort to driving the well to incipient failure.